LIII. But be it as it may, with respect to this difficulty, and all others, which the moderns by virtue of their principles can oppose to the doctrine of Aristotle; it is certain, that there may be very serious ones urged against their definition of living entities. Heavy bodies move _ab intrinsico_, and are not living entities. Fire moves _ab intrinsico_, and is not a living entity. The fermentative motion also, according to common physics, is understood to be _ab intrinsico_. And I have remarked and proved in another part of this work, that what the Aristotelites say of heavy bodies being moved by communicated impulse, in the form this explanation is intelligible, is also applicable to the motion of living entities. SECT. XIII. LIV. There now only remains within the compass of the predicamental scale, one other thing to consider, which is the highest, and most sublime within the reach of physics, and that is, the nature and composition of the body; but where will this lead us to, the point being equally doubtful with all the rest? The composition of the body, is divided into elemental and mixed; but as this last is composed of the other, unless we know what the elemental is, it is impossible to know of what the mixture consists. Very well; but who knows the nature and number of the elements? To this question, methinks I hear four answers, from four sects of philosophers, which are all different, although each pretends to exclude the others from a competent knowledge of the matter. The Aristotelites say, that they are air, fire, earth, and water. The chymists, that they are salt, sulphur, mercury, earth, and water. The Cartesians insist, that they are composed of the subtil, the globulous, and another matter which is more gross, and which they call the third element; and the atomists, that they consist of the atoms. These are the opinions, which are at present the most prevailing, although there are numbers of others which I shall omit to mention, because they have but few votaries. Now which of these opinions is the true one? Perhaps neither. At least there is but one sect out of the four that admits either of them to be true, and whichever that sect adheres to, the other three assert to be false; which amounts to the same, as saying that one witness deposes to the truth of the matter in question, and that three give testimony against it. Thus no judge to whom the decision is confided, can give sentence in favour of either of the parties; it being out of his power to affirm, that any one of their systems is right and true.